SALT MARSHES -PAST AND FUTURE 



prepared a chart of Salem and Marblehead 

 liarbors, giving the soundings over various 

 ledges and rocks. Ninety years later, in 1894, 

 carefxil measurements were again made at 

 these same points and under similar condi- 

 tions of tide and moon, by the late Professor 

 John H. Sears. In all cases the water was 

 found to be from one to two feet deeper than 

 it was ninety years before. In 1903 Mr. John 

 R. Freeman concluded that the land in Boston 

 and vicinity was sinking at the rate of a foot 

 in a hundred years by comparison with vari- 

 ous ancient and modern tide gauges; also by 

 the fact that the sills and floors of the masonry 

 dry dock at the Charlestown Navy Yard then 

 stood about nine inches lower relatively to 

 mean sea level than they did seventy years 

 before, while the dock stood at precisely the 

 same level relatively to points on solid ground. 

 An incontestable evidence of a former 

 higher land level is presented by the deep 

 channels of all our eastern rivers, up which 

 the tide rushes for many miles, and by the fact 

 that these channels extend for a long distance 

 out to seaward under the water. Only when 

 the land stood at a much higher level could 

 these channels have been cut. 



213 



